The present invention relates to a filter for filtering suspension under pressure and discontinuously exhausting a filter cake having low content of a mother liquor.
In a well-known filter system, a filter cloth is disposed on a filter plate provided on the upper surface of a flat filter medium support, and a cover arranged above the filter plate is brought into tight contact with the circumferential portion of the filter plate. Then, suspension is supplied under pressure to a space defined between the cover and the filter cloth to carry out filtration. When filtration efficiency is reduced because of stacking of a filter cake on the filter cloth, supply of the suspension is stopped, and pressure air is supplied to reduce mother liquor content of the filter cake. Then, the cover is separated from the filter plate to remove the filter cake as well as the filter cloth. Further, in another well-known filter system, a long filter cloth is used, and a predetermined length of the filter cloth is moved every time filtering operation is carried out to thereby remove the filter cake. Furthermore, the operation of separating the cover from the filter plate is carried out by using a fluidic cylinder.
It has been proposed that such a filtration dewatering system is intended to be operated automatically with no hands. However, the conventional automatic operating system is generally a sequence control system wherein an operating signal is simply generated and stopped according to lapse of a set time, or a sequence control system wherein a sensor for detecting the end of the operation of the system is used, and after one step terminates, the subsequent step automatically starts.
On the other hand, the use of pneumatic equipment is greater in comparison with a hydraulic equipment because of easiness of piping for fluid and reduced pollution to working environment irrespective of the disadvantage that the pneumatic equipment is low in response speed and power output. When using pneumatic equipment, it is necessary to make the cylinder large to reduce the foregoing disadvantages and correspondingly to make air pipings and valves still larger, which results in economical disadvantages. Further, control speed is limited because of slow response.